For a long time, a direct drive of a horizontally arranged mill body has been provided in so-called mill drives, such as are used for milling cement or ores, in particular copper ores. For this purpose, the dynamo-electric drive motor is arranged concentrically with respect to the mill body, wherein the rotor and stator have comparatively large diameters in the region of greater than 5 m (U.S. Pat. No. 3,272,444).
At the same time, the rotor shaft is formed by the mill body itself, which is provided with a ring flange for fixing the active rotor parts. At the same time, the rotor has several segments, which carry one or more magnetic poles. Each of these segments is provided with a supporting ligament which runs in the circumferential direction of the rotor and is mechanically connected to the ring flange of the mill body.
The primary component of a ring motor of this kind, the stator, is designed for energizing with electric current. For this 7 purpose, it has a winding system distributed over the slots of the stator. As described above, the secondary component has individual rotor segments which are provided with permanent magnets or windings which can be energized. The ring motor therefore has a primary component and a secondary component, each having active magnetic means which can be called upon to generate a magnetic field. Examples of active magnetic means are windings that can be energized, permanent magnets or windings in which an electrical current flow can be produced by means of induction, wherein a magnetic field can be generated by means of the electrical current flow that can be produced.
A disadvantage, particularly because of the comparatively large dimensions of these direct drives, is the assembly on site, as the components, such as stator or rotor, cannot be transported as a complete arrangement. The stator and rotor of the direct drive must therefore also be divided into segments to obtain suitable dimensions for transportation. Accordingly, assembly on site is difficult, as a predominant part of the winding systems must be fitted into the stator slots, insulated and tested on site. Likewise, positioning the active magnetic means on the rotor necessitates laborious and therefore time-consuming assembly.
Because, among other things, of the increased dielectric requirements imposed on the winding systems, the application of operationally suitable insulation outside the factory is also problematic, for one thing because of the dust-laden environment.